1. Field of the Invention
The field of the present invention is the manufacture of multi-layer web products, particularly web products made from nonwoven fibers.
2. Background
Consumers tend to prefer nonwoven web products made from long fibers because of their superior hand feel as compared to short fibers such as wood pulp. Unfortunately, long fiber web products are generally more expensive than short fiber web products. Therefore, in order to meet the demands of consumers by providing a web product having a superior hand feel and meet the needs of manufacturers by reducing costs of materials and production, web products that include a combination of long and short fibers have been developed.
FIG. 1 schematically illustrates a prior art apparatus for manufacturing wet laid fibrous web products using in-line hydroentanglement. The fibers are opened, treated, blended, diluted, and refined as necessary at the pre-treatment stage 50 of the apparatus to form the furnish. To provide a product having a hand feel that is superior to short fiber products, the furnish is formed from a combination of short and long fibers mixed together (throughout this description of the background and the description of the preferred embodiment of the invention, short fibers are typically natural fibers, but may also be or include synthetic fibers, while long fibers are typically synthetic fibers, but may also be or include natural fibers). From the pre-treatment stage 50, the furnish is directed into the head box 51, from which the fibers are deposited as a web onto the forming wire 52. Once on the forming wire 52, the web is conveyed to the hydroentanglement unit 53, which directs high pressure water streams at the web to entangle the fibers. Depending upon the final web properties desired, the web may be transported under the hydroentanglement unit multiple times or under a hydroentanglement unit with multiple hydroentangling heads, or the web may be turned over to direct the high pressure water at the other side of the web. Following hydroentanglement, a drying unit 54 dries the web using any number of conventional drying processes, such as steam heated can dryers, TAD (through air drying), or Radiant Heat (such as Infra-Red). After drying, the web is wound into a roll 55 for storage or subsequent processing.
The combination web products produced using the apparatus of FIG. 1 exhibit cost savings over all long fiber products. At the same time, such products come closer to providing, but do not reach, the superior hand feel associated with all long fiber products.
Two-layer web products have also been developed. Such web products have a first layer of short fibers and a second layer of long fibers. FIGS. 2-4 schematically illustrate prior art apparatuses for manufacturing two-layer web products. The apparatus of FIG. 2 is employed to manufacture a single layer wet laid short fiber web product. Such a short fiber web product is used as the first layer of a two-layer web product in a downstream process. In brief, the short fibers are separated, treated, blended, diluted and refined as necessary at the pre-treatment stage 60 of the apparatus to form the furnish. From the pre-treatment stage 60, the furnish is directed into the head box 61, from which the fibers are deposited onto the forming wire 62. A drying unit 63 dries the web and the dried web is wound into a roll 64 pending subsequent processing.
The apparatus of FIG. 3 is employed to manufacture a single layer long fiber web product. Such a long fiber product is used as the second layer of a two-layer web product in a downstream process. The web formed with this apparatus typically uses longer fibers (generally 25 to 45 mm, or longer such as 45 to 100 mm). The long fibers are pre-opened in the bale opener 70 and transported to the fine opener 71. Once the fibers are sufficiently separated and declumped for final processing and forming, they are transported to the chute feed 72 which meters them at a uniform rate and volume onto the feed roll 73 and then the lickerin roll 74. The lickerin roll 74 transfers fibers in a separated, uniform, and controlled manner to the main carding cylinder 75. The fibers are repeatedly combed and stripped from the main carding cylinder 75 by the worker and stripper rolls 76. A combing cylinder 77 is positioned to comb the web from the main carding cylinder 75 and transfer the web to the doffer cylinder 78 (which also serves to comb the web). The web is transferred from the doffer cylinder 78 onto the forming wire 82. Once on the forming wire 82, the web is passed under a hydroentanglement unit 79 and through the drying unit 80. The dried web is wound into a roll 81 pending subsequent processing.
The long fiber web product created by the process of FIG. 3 may be substituted with a two-layer long fiber web product through implementation of the carding apparatus disclosed in European Patent Application EP 1046731 A1, the disclosure of which is incorporated herein by reference. With such a carding apparatus, two webs are combed from the main carding cylinder, recombined, and joined either through entanglement or light adhesive bonding. Subsequent processing of both one- and two-layer long fiber webs may be performed in the same manner.
The apparatus of FIG. 4 is employed to combine a short fiber web with a long fiber web into a two-layer web product. A long fiber web, such as one made by the apparatus of FIG. 3, is unwound from a roll 81 onto a carrier wire 82. A short fiber web, such as one made by the apparatus of FIG. 2, is unwound from a roll 64 and laid upon the long fiber web. The two webs are passed under a hydroentanglement unit 90, through a dryer unit 92, and wound into a roll 93.
The two-layer web products produced using the apparatuses of FIGS. 2-4 also exhibit cost savings over all long fiber products. However, because only one side of such web products exhibits the superior hand feel of long fibers, while the other side exhibits the less desired hand feel of short fibers, such a product does not meet with the same consumer demand as does an all long fiber web product.
FIGS. 2-4 illustrate an off-line process of manufacturing the two-layer web product. In practice, however, the apparatuses of FIGS. 2-4 are combinable for in-line formation of the two-layer web product.
U.S. Pat. No. 6,110,848, the disclosure of which is incorporated herein by reference, teaches a three-layer web product and the production thereof. This three-layer web product goes further toward meeting the demands of consumers and the cost needs of manufacturers, as it includes two outer layers of long fiber and a middle layer sandwiched therebetween of short fiber. The apparatus of FIG. 5 is employed to manufacture such a three-layer web product. A first long fiber web is unwound from a roll 81 onto a carrier wire 91. A short fiber web is unwound from a second roll 69 and laid upon of the first long fiber web. A second long fiber web is unwound from a roll 81 and laid upon the short fiber web, thereby sandwiching the short fiber web between two layers of long fiber. This three-layer structure conveyed under a hydroentanglement unit 90 and through a drying unit 92. As with other prior art, hydroentanglement of the three-layer web may be done with multiple passes, multiple heads, or on both sides of the web. The dried web is wound into a roll 104 pending further processing.
The three-layer web product is superior to other prior art web products that combine long and short fibers because it has the superior hand feel on both sides of the product and the product may be bulked up with short fiber as the middle layer without effecting the hand feel on either side of the product.
The apparatus of FIG. 6 illustrates the process of FIG. 5 as an in-line process. The long fiber forming equipment, labeled as C1 and C2, respectively, up to the doffer cylinder 78, is the same as described in connection with FIG. 3. A first long fiber web from the first forming equipment C1 is laid upon the forming wire 125. Short fiber deposition equipment S1 deposits short fiber upon the first long fiber web. The short fiber, whether from a roll or otherwise, is fed into a hammermill 121 which separates the fibers. A transport fan 122 sends the separated short fibers to the forming heads 123, where the short fibers are blown onto the first long fiber web. Vacuum suction units 124 on the opposite side of the forming wire 125 from the forming heads 123 assist in forming the layer of short fibers on the first long fiber web. The second long fiber web from the second forming equipment C2 is laid on top of the short fibers. The three-layer structure is passed under the hydroentanglement unit 79, through the drying unit 80, and wound into a roll 105 pending subsequent processing.
Such an in-line process has the additional cost benefit of reducing or eliminating the need to store intermediary rolls. However, even with these advances in the production of nonwoven web products where 1) the products better meet the demands of consumers and 2) the manufacturing costs have been reduced, the costs of producing such web products remains high and would significantly benefit from apparatuses and processes which serve to further reduce production costs.